pgtools/pgmanager.py
author Radek Brich <radek.brich@devl.cz>
Wed, 20 Jul 2011 10:51:18 +0200
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# -*- coding: utf-8 -*-
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#
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# PgManager - manage database connections
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#
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# Requires: Python 2.6, psycopg2
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#
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# Copyright (c) 2010, 2011  Radek Brich <radek.brich@devl.cz>
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#
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# Permission is hereby granted, free of charge, to any person obtaining a copy
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# of this software and associated documentation files (the "Software"), to deal
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# in the Software without restriction, including without limitation the rights
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# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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# copies of the Software, and to permit persons to whom the Software is
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# furnished to do so, subject to the following conditions:
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#
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# The above copyright notice and this permission notice shall be included in
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# all copies or substantial portions of the Software.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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# THE SOFTWARE.
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"""Postgres database connection manager
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PgManager wraps psycopg2 connect function, adding following features:
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 * Manage database connection parameters - link connection parameters
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   to an unique identifier, retrieve connection object by this identifier
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 * Connection pooling - connections with same identifier are pooled and reused
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 * Easy query using the with statement - retrieve cursor directly by connection
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   identifier, don't worry about connections
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 * Dict rows - cursor has additional methods like fetchall_dict(), which
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   returns dict row instead of ordinary list-like row
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Example:
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import pgmanager
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pgm = pgmanager.get_instance()
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pgm.create_conn(hostaddr='127.0.0.1', dbname='postgres')
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with pgm.cursor() as curs:
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    curs.execute('SELECT now() AS now')
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    row = curs.fetchone_dict()
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    print row.now
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First, we have obtained PgManager instance. This is like calling
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PgManager(), although in our example the instance is global. That means
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getting the instance in another module brings us all the defined connections
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etc.
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On second line we created connection named 'default' (this name can be left out).
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The with statement obtains connection (actually connects to database when needed),
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then returns cursor for this connection. On exit, the connection is returned
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to the pool or closed (depending on number of connections on pool and setting
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of keep_open parameter).
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The row returned by fetchone_dict() is special dict object, which can be accessed
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using item or attribute access, that is row['now'] or row.now.
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"""
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from contextlib import contextmanager
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import logging
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import threading
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import select
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import psycopg2
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import psycopg2.extensions
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from psycopg2 import DatabaseError, IntegrityError
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class PgManagerError(Exception):
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    pass
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class ConnectionInfo:
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    def __init__(self, dsn, isolation_level=None, init_statement=None, keep_open=1):
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        self.dsn = dsn
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        self.isolation_level = isolation_level
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        self.init_statement = init_statement
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        self.keep_open = keep_open
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class RowDict(dict):
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    def __getattr__(self, key):
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        return self[key]
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class Cursor(psycopg2.extensions.cursor):
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    def execute(self, query, args=None):
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        try:
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            return super(Cursor, self).execute(query, args)
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            log.debug(self.query.decode('utf8'))
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    def callproc(self, procname, args=None):
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        try:
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            return super(Cursor, self).callproc(procname, args)
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            log.debug(self.query.decode('utf8'))
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    def row_dict(self, row, lstrip=None):
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        adjustname = lambda a: a
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        if lstrip:
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            adjustname = lambda a: a.lstrip(lstrip)
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        return RowDict(zip([adjustname(desc[0]) for desc in self.description], row))
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    def fetchone_dict(self, lstrip=None):
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        row = super(Cursor, self).fetchone()
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        if not row:
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            return row
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        return self.row_dict(row, lstrip)
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    def fetchall_dict(self, lstrip=None):
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        rows = super(Cursor, self).fetchall()
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        return [self.row_dict(row, lstrip) for row in rows]
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class Connection(psycopg2.extensions.connection):
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    def cursor(self, name=None):
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        if name is None:
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            return super(Connection, self).cursor(cursor_factory=Cursor)
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        else:
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            return super(Connection, self).cursor(name, cursor_factory=Cursor)
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class PgManager:
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    def __init__(self):
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        self.conn_known = {}  # available connections
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        self.conn_pool = {}
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        self.lock = threading.Lock()
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    def __del__(self):
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        for conn in tuple(self.conn_known.keys()):
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            self.destroy_conn(conn)
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    def create_conn(self, name='default', isolation_level=None, dsn=None, **kw):
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        '''Create named connection.'''
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   153
        if name in self.conn_known:
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   154
            raise PgManagerError('Connection name "%s" already registered.' % name)
0
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   155
eaae9539e910 Postgres tools.
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   156
        if dsn is None:
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   157
            dsn = ' '.join([x[0]+'='+str(x[1]) for x in kw.items()])
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   158
eaae9539e910 Postgres tools.
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        isolation_level = self._normalize_isolation_level(isolation_level)
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   160
        ci = ConnectionInfo(dsn, isolation_level)
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   161
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        self.conn_known[name] = ci
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   163
        self.conn_pool[name] = []
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   164
eaae9539e910 Postgres tools.
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   165
    def close_conn(self, name='default'):
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   166
        '''Close all connections of given name.
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   167
        
eaae9539e910 Postgres tools.
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   168
        Connection credentials are still saved.
eaae9539e910 Postgres tools.
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diff changeset
   169
        
eaae9539e910 Postgres tools.
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   170
        '''
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   171
        while len(self.conn_pool[name]):
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   172
            conn = self.conn_pool[name].pop()
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   173
            conn.close()
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   174
eaae9539e910 Postgres tools.
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   175
    def destroy_conn(self, name='default'):
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   176
        '''Destroy connection.
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   177
        
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        Counterpart of create_conn.
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   179
        
eaae9539e910 Postgres tools.
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   180
        '''
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   181
        if not name in self.conn_known:
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   182
            raise PgManagerError('Connection name "%s" not registered.' % name)
0
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   183
eaae9539e910 Postgres tools.
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   184
        self.close_conn(name)
eaae9539e910 Postgres tools.
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diff changeset
   185
eaae9539e910 Postgres tools.
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   186
        del self.conn_known[name]
eaae9539e910 Postgres tools.
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   187
        del self.conn_pool[name]
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   188
eaae9539e910 Postgres tools.
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   189
    def get_conn(self, name='default'):
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   190
        '''Get connection of name 'name' from pool.'''
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   191
        self.lock.acquire()
eaae9539e910 Postgres tools.
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   192
        try:
eaae9539e910 Postgres tools.
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   193
            if not name in self.conn_known:
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   194
                raise PgManagerError("Connection name '%s' not registered." % name)
0
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   195
eaae9539e910 Postgres tools.
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   196
            conn = None
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   197
            while len(self.conn_pool[name]) and conn is None:
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   198
                conn = self.conn_pool[name].pop()
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   199
                if conn.closed:
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   200
                    conn = None
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diff changeset
   201
eaae9539e910 Postgres tools.
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diff changeset
   202
            if conn is None:
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   203
                ci = self.conn_known[name]
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   204
                conn = psycopg2.connect(ci.dsn, connection_factory=Connection)
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   205
                if not ci.isolation_level is None:
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   206
                    conn.set_isolation_level(ci.isolation_level)
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diff changeset
   207
                if ci.init_statement:
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   208
                    curs = conn.cursor()
eaae9539e910 Postgres tools.
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   209
                    curs.execute(ci.init_statement)
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diff changeset
   210
                    curs.close()
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diff changeset
   211
        finally:
eaae9539e910 Postgres tools.
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   212
            self.lock.release()
eaae9539e910 Postgres tools.
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   213
        return conn
eaae9539e910 Postgres tools.
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   214
eaae9539e910 Postgres tools.
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diff changeset
   215
    def put_conn(self, conn, name='default'):
eaae9539e910 Postgres tools.
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diff changeset
   216
        '''Put connection back to pool.
eaae9539e910 Postgres tools.
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diff changeset
   217
        
eaae9539e910 Postgres tools.
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   218
        Name must be same as used for get_conn,
eaae9539e910 Postgres tools.
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   219
        otherwise things become broken.
eaae9539e910 Postgres tools.
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diff changeset
   220
        
eaae9539e910 Postgres tools.
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diff changeset
   221
        '''
eaae9539e910 Postgres tools.
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   222
        self.lock.acquire()
eaae9539e910 Postgres tools.
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parents:
diff changeset
   223
        try:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   224
            if not name in self.conn_known:
2
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diff changeset
   225
                raise PgManagerError("Connection name '%s' not registered." % name)
0
eaae9539e910 Postgres tools.
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parents:
diff changeset
   226
eaae9539e910 Postgres tools.
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diff changeset
   227
            if len(self.conn_pool[name]) >= self.conn_known[name].keep_open:
eaae9539e910 Postgres tools.
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diff changeset
   228
                conn.close()
eaae9539e910 Postgres tools.
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diff changeset
   229
                return
eaae9539e910 Postgres tools.
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parents:
diff changeset
   230
eaae9539e910 Postgres tools.
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diff changeset
   231
            if conn.get_transaction_status() == psycopg2.extensions.TRANSACTION_STATUS_UNKNOWN:
eaae9539e910 Postgres tools.
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parents:
diff changeset
   232
                conn.close()
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   233
                return
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   234
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   235
            # connection returned to the pool must not be in transaction
eaae9539e910 Postgres tools.
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parents:
diff changeset
   236
            if conn.get_transaction_status() != psycopg2.extensions.TRANSACTION_STATUS_IDLE:
eaae9539e910 Postgres tools.
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parents:
diff changeset
   237
                conn.rollback()
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   238
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   239
            self.conn_pool[name].append(conn)
eaae9539e910 Postgres tools.
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parents:
diff changeset
   240
        finally:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   241
            self.lock.release()
eaae9539e910 Postgres tools.
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parents:
diff changeset
   242
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   243
    @contextmanager
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   244
    def cursor(self, name='default'):
eaae9539e910 Postgres tools.
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diff changeset
   245
        '''Cursor context.
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   246
        
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   247
        Uses any connection of name 'name' from pool
eaae9539e910 Postgres tools.
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diff changeset
   248
        and returns cursor for that connection.
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   249
        
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
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diff changeset
   250
        '''
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
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diff changeset
   251
        conn = self.get_conn(name)
eaae9539e910 Postgres tools.
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parents:
diff changeset
   252
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   253
        try:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   254
            curs = conn.cursor()
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   255
            yield curs
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   256
        finally:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   257
            curs.close()
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   258
            self.put_conn(conn, name)
eaae9539e910 Postgres tools.
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parents:
diff changeset
   259
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   260
    def wait_for_notify(self, name='default', timeout=5):
eaae9539e910 Postgres tools.
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parents:
diff changeset
   261
        '''Wait for asynchronous notifies, return the last one.
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   262
        
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   263
        Returns None on timeout.
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   264
        
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   265
        '''
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   266
        conn = self.get_conn(name)
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   267
        
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   268
        try:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   269
            # any residual notify?
eaae9539e910 Postgres tools.
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parents:
diff changeset
   270
            # then return it, that should not break anything
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   271
            if conn.notifies:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   272
                return conn.notifies.pop()
eaae9539e910 Postgres tools.
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parents:
diff changeset
   273
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   274
            if select.select([conn], [], [], timeout) == ([], [], []):
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   275
                # timeout
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   276
                return None
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   277
            else:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   278
                conn.poll()
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   279
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   280
                # return just the last notify (we do not care for older ones)
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   281
                if conn.notifies:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   282
                    return conn.notifies.pop()
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   283
                return None
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   284
        finally:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   285
            # clean notifies
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   286
            while conn.notifies:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   287
                conn.notifies.pop()
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   288
            self.put_conn(conn, name)
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   289
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   290
    def _normalize_isolation_level(self, level):
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   291
        if type(level) == str:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   292
            if level.lower() == 'autocommit':
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   293
                return psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   294
            if level.lower() == 'read_committed':
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   295
                return psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   296
            if level.lower() == 'serializable':
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   297
                return psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE
eaae9539e910 Postgres tools.
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parents:
diff changeset
   298
            raise PgManagerError('Unknown isolation level name: "%s"', level)
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   299
        return level
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   300
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   301
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   302
try:
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
parents:
diff changeset
   303
    NullHandler = logging.NullHandler
eaae9539e910 Postgres tools.
Radek Brich <radek.brich@devl.cz>
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except AttributeError:
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    class NullHandler(logging.Handler):
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        def emit(self, record):
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            pass
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log = logging.getLogger("pgmanager")
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log.addHandler(NullHandler())
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instance = None
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def get_instance():
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    global instance
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    if instance is None:
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        instance = PgManager()
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    return instance
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